1. Field of the Invention
The present invention relates to a cover film for a printed circuit board, and more particularly, to a cover film having a composite material layer with low gloss applicable to a printed circuit board, which needs circuit shield.
2. Description of Related Art
Printed circuit boards are essential components in electrical products. Printed circuit boards are in high demand as the increased demand of commercial electrical products. Flexible printed circuit boards are flexible for 3D wiring, so as to be widely used in computers, communication products, commercial electrical products and the like which need to be thin and small.
Generally, flexible printed circuit boards are formed by flexible copper clad laminates (FCCL) and cover films (CL). A plastic film is used as or a thin insulating ink layer is printed as a cover film for a printed circuit board. However, ink cracks in the conventional cover films. Currently, most cover films in the market are bright polyimide thin film. In order to form a polyimide film applicable to layout of shield circuits, a black adhesive layer 12 is formed on a polyimide thin film 11 as shown in FIG. 1A. However, the surface of the polyimide thin film is still too bright, and thus fails to meet the requirement in specific optical application.
There is another polyimide film as shown in FIG. 1B. A black polyimide thin film 11a has carbon powder, and an adhesive layer 12a is formed on the black polyimide thin film 11a. This polyimide film has better anti-glare effect, but has high cost. The polyimide films with additives have poor anti-tensile strength and size stability.
Therefore, there is a need to develop a cover film having low cost, good anti-glare effect and great folding endurance.